Coating method



United States Patent COATING METHOD Raymond G. Townsend, Scotia, N.Y., assiguor to the United States of America as represented by the United States Atomic Energy Commission N0 Drawing. Application May 23, 1951 Serial No. 227,935

1 Claim. (Cl. 204-38) This invention relates to a method of protectively coating beryllium metal and more particularly to a method for applying a protective layer of chromium to beryllium metal.

The nuclear and physical properties of beryllium are such that it has been used extensively in nuclear reactors and further extensive use of this material seems quite probable. A proposed application is the moderating material in liquid metal cooled nuclear reactors. In this application, however, some method must be found for protecting the beryllium since liquid metals such as the alkali metals and their alloys which are being considered as coolants attack beryllium at the elevated temperatures at which such reactors will operate.

It is an object of this invention to form a protective coating upon beryllium metal. It is a further object to form a firmly bonded protective coating upon beryllium metal. A still further object is to form a non-porous coating upon beryllium that will resist the corrosive attack of liquid metals at elevated temperatures.

These objects are accomplished in the present invention by applying a chromium plate to the beryllium. The following example gives a preferred embodiment of the present invention.

Example: A test specimen of beryllium 2 inches long and k inch in diameter was prepared. This specimen was chemically etched for 2 minutes in a bath maintained at 110 F. and containing orthophosphoric acid 85% by weight, chromic anhydride 7% by weight and sulfuric acid (concentrated) 8% by weight. The specimen was then rinsed in cold water and immersed for 30 seconds in a solution of sodium zincate (a solution containing 500 grams of sodium hydroxide and 100 grams of zinc oxide per liter) at 100 F. The specimen was again rinsed in cold water and immersed for seconds in 60% nitric acid. Following another rinse in cold Water, the specimen was again immersed in sodium zincate solution for 30 seconds and rinsed again in cold water. A copper plate was then applied to the specimen by plating it for 3 minutes in a cyanide-copper plating bath. After rinsing with cold water, the specimen was chrome plated in a 100-1 chromic acid-sulfate plating bath until a layer of about 0.5 mil of chrome was obtained.

2,901,408 Patented Aug. 25, 1959 This specimen was placed in a bath of liquid sodium at 500 C. for one month. It was found that the specimen during this period had gained weight to the extent of only 0.02 mg./cm. /month which was so slight as to be within the limits of allowable weighing error.

The zinc and copper layers were not. evident in micro examination of a section of the plated sample indicating that they must have alloyed with the beryllium during the testing process. It was not possible to mechanically peel the plated layer from the beryllium.

While the foregoing example illustrates a preferred embodiment of the present invention, it should be apparent that it may be departed from in some respects. For example, beryllium which is excessively corroded should be etched in 1-1 hydrochloric acid prior to the immersion in the chemical cleaning solution which comprised the first step of the above example. If a uniform and adherent coating of zinc is obtained in the first immersion of the beryllium in the sodium zincate solution, the nitric acid immersion and the second sodium zincate immersion may be eliminated. A zinc phosphate solution has been used instead of the sodium zincate but has not proved to be quite as satisfactory and the sodium zincate treatment is recomended.

The copper plate may be applied in any bath that will give a bright flash of copper over the zinc layer. However, it has been found that the copper layer is absolutely necessary to obtain a satisfactory coating of chromium. A copper layer of about 0.1 mil appears satisfactory. It has also been found that other types of chrome plating baths are satisfactory. The only criteria is that a dense and uniform coating of chrome of from about 0.15 to 0.5 mil be obtained over the copper layer.

It will be seen that the present invention affords a simple, inexpensive and efiicient process for obtaining a protective coating upon beryllium. While a preferred embodiment and certain modifications of the present invention have been described above, other modifications will be apparent to those skilled in the art, and the invention is to be limited only by the prior art and the scope of the appended claim.

I claimr A method of protectively coating beryllium metal which comprises the steps of etching said metal in an acid bath, immersing the etched beryllium in a solution of sodium zincate for a brief period of time, immersing the beryllium in concentrated nitric acid, immersing the beryllium in a second solution of sodium zincate, electroplating a thin layer of copper over said beryllium, and finally electroplating a layer of chromium over said copper layer.

Stareck et a1 June 20, 1950 Kolodney Mar. 11, 1952 

